Multiple stage hydrocracking process

ABSTRACT

A SULFUROUS CHARGE STOCK, CONTAINING NITROGENOUS COMPOUNDS AND AROMATIC HYDROCARBONS, IS CONVERTED INTO LOWER-BOILING HYDROCARBON PRODUCTS OF PREDETERMINED END BOILING POINTS. THE CHARGE STOCK, IN ADMIXTURE WITH A PREVIOUSLY HYDROCRACKED, SUBSTANTIALLY DESULFURIZED STREAM, IS SUBJECTED TO A CLEAN-UP OPERATION AT RELATIVELY LOW OPERATING SEVERITIES FOR THE REMOVAL OF NITROGENOUS COMPOUNDS WITHOUT INCURRING THE FORMATION OF APPRECIABLE QUANTITIES OF POLYNUCLEAR AROMATICS. FOLLOWING SEPARATION, A PORTION OF THE SUBSTANTIALLY NITROGEN-FREE PRODUCT IS THEN SUBJECTED TO HYDROCRACKING WITHOUT INCURRING RAPID CATALYST DEACTIVATION NORMALLY RESULTING FROM THE PRESENCE OF CONDENSED RING, POLYNUCLEAR AROMATICS.

y 13, 1971 E. L. POLLITZER 3,592,759

MULTIPLE STAGE HYDROCRACKING PROCESS Filed April 18. 1969 ReactorProduct Separation //Vl E/V TOR: E rnesf L. Poll/'rzer Q/zidzur- 4 2AZQ'M ATTORNEYS United States Patent 3,592,759 MULTIPLE STAGEHYDROCRACKING PROCESS Ernest L. Pollitzer, Skokie, Ill., assignor toUniversal Oil Products Company, Des Plaines, Ill. Filed Apr. 18, 1969,Ser. No. 817,533 Int. Cl. Cg 23/00 U.S. Cl. 208-89 6 Claims ABSTRACT OFTHE DISCLOSURE APPLICABILITY OF INVENTION In its broad sense, thepresent invention involves the conversion of hydrocarbonaceous mixturesinto lowerboiling hydrocarbon products. More specifically, the inventiveconcept herein described encompasses a process for hydrocrackinghydrocarbonaceous mixtures containing aromatic hydrocarbons andcontaminated by sulfurous and nitrogenous compounds. Through theutilization of my invention, the interference, with catalytic activity,experienced as a result of the simultaneous presence of sulfur, nitrogenand aromatic hydrocarbons is significantly decreased.

Suitable charge stocks, to the processing and conversion of which thepresent invention is applicable, are generally classified into a varietyof categories. These include gasoline boiling range fractions, bothlight naphtha and heavy naphtha, kerosene fractions, gas oil fractions,heavy vacuum gas oil distillates, and even heavier hydrocarbonaceousmaterial boiling up to a temperature of about 1050 F. The quality of thedesired lower-boiling hydrocarbon product is generally dependent uponthe character of the charge stock. For example, light naphtha and othergasoline boiling range distillates will often be converted intosubstantial quantities of LPG (liquefied petroleum gas). Light and heavygas oils are generally processed to produce gasoline ormiddle-distillate boiling range fractions. As is well-known to thosehaving expertise in petroleum refining techniques, various combinationsof product streams may be desired depending upon the particular localeand marketing needs and demands. For example, a heavy charge stock,boiling from about 850 F. to about 1050 P. will often be processed in amanner which produces maximum quantities of both LPG and a gasolineboiling range fraction. It is understood that the present invention isnot considered to be limited to a particular charge stock from which itis desired to produce a particular product slate.

The charge stocks processed in accordance with the 3,592,759 PatentedJuly 13, 1971 ice present invention contain condensed ring aromatics,simpler, mononuclear aromatics, or their partially hydrogenatedderivatives, as well as alkyl-substituted aromatic hydrocarbons.Depending upon the boiling range of the particular charge stock, thequantity of aromatic hydrocarbons can vary from about 5.0% to about60.0% by volume. Likewise, those charge stocks intended for conversioninto lower-boiling hydrocarbon products contain substantial quantitiesof sulfurous compounds, often ranging as high as 5.0% by weight,calculated as elemental sulfur. The quantity of nitrogenous compoundswill generally vary as the boiling range of the charge stock and itssource, and can be as low as about 25 p.p.m., and as high as about 6,000ppm, calculated as nitrogen by weight. Prior to becoming suitable fortheir intended use, the lower-boiling products must necessarily besubstantially, completely free from nitrogen and sulfur. A commonpractice is to subject such material to a hydrotreating unit (oftenreferred to as hydrofining) in order to prepare a substantially cleancharge stock for subsequent processing in a hydrocracking unit. Thesehydrotreating or hydrorefining processes are generally conductedcatalytically at temperatures of about 700 F. to about 800 F, asmeasured at the inlet to the catalyst bed. It has been found thatexcellent nitrogen and sulfur removal results, even with heavier chargestocks, but the severity of operation leads to considerable formation ofpolynuclear aromatics which are effective catalyst poisons in anysubsequent hydrocracking operation. Indications also exist that thenitrogenous compounds actually foster the formation of polynucleararomatics such that an effective clean-up operation results inadditional polynuclear aromatics being charged to the hydrocrackingreaction zone. The anomaly is obvious: the desired product must besubstantially sulfur and nitrogen free; nitrogen and aromatichydrocarbons should not co-exist within the process in an atmosphereconducive to the formation of polynuclear aromatics; and, at least asubstantial portion of the virgin aromatics present in the fresh feedcharge stock should be hydrogenated. These aromatics interfere, and areotherwise detrimental to hydrocracking in several ways. Condensed ringaromatics actually serve as a catalyst poison to the extent that thedesired hydrocracking reactions are inhibited to an undesirable degree.Furthermore, the mononuclear aromatics, or their partially hydrogenatedderivatives, can condense to produce additional polynuclear compounds.It should also be noted that the hydrogenation of aromatic hydrocarbonsinvolves a high heat of reaction which in turn favors the undesiredcondensation side reactions.

Briefly, the process encompassed by the present invention involves theinitial removal of nitrogenous compounds at relatively low severitieswhich are not as conducive to the formation of polynuclear aromatics,hydrocracking at an elevated operating severity and desulfurization atan intermediate operating severity.

OBJECTS AND EMBODIMENTS An object of the present invention is to converta hydrocarbon charge stock into lower-boiling hydrocarbon products. Acorollary objective involves hydrocracking a sulfurous charge stockcontaining nitrogenous compounds and aromatic hydrocarbons, intolower-boiling hydrocarbon products, without incurring the rapiddeactivation of the catalytic composite otherwise resulting from thesimultaneous presence of nitrogenous compounds and aromatichydrocarbons.

Another object of my invention is to provide a multiple-stage, fixed-bedcatalytic system in which the hydrocracking of hydrocarbonaceousmaterial is facilitated.

Therefore, in one embodiment, my invention provides a catalytic processfor converting a sulfurous charge stock, containing nitrogeous compoundsand aromatic hydrocarbons, into lower-boiling hydrocarbon products of apredetermined end boiling point, which process comprises the steps of:(a) reacting a substantially nitrogen-free portion of said charge stock,and hydrogen in a first reaction zone, in contact with a first catalyticcomposite, at conversion conditions including a maximum catalyst bedtemperature of 800 F. to about 900 F.; (b) introducing the resultingfirst zone effluent into a second reaction zone, and reacting the same,in contact with a second catalytic composite, at desulfurizationconditions including a maximum catalyst bed temperature of 700 F. toabout 800 F.; (c) introducing said charge stock and the resulting secondzone efiluent into a third reaction zone, and reacting the same andhydrogen, in contact with a third catalytic composite, at conditionsincluding a maximum catalyst bed temperature of about 650 F. to about725 F., and selected to convert nitrogenous compounds; (d) separatingthe third reaction zone efiiuent to provide a hydrogen-rich vaporousphase, to recover said lower-boiling products and to provide a normallyliquid hydrocarbon stream boiling above said predetermined end boilingpoint and containing said nitrogen-free portion of said charge stock;and, (e) reacting said normally liquid stream in said first reactionzone.

Other objects and embodiments of my invention will become evident fromthe following, more detailed description thereof. These involvepreferred catalytic composites, operating conditions and variousoperating techniques.

SUMMARY OF INVENTION As hereinbefore set forth, the present invention isdirected toward a multiple-stage hydrocracking process wherein thecharge stock contains aromatic hydrocarbons, nitrogenous compounds andsulfurous compounds. The hydrocracking process, encompassed by myinvention, is a catalytic process, preferably conducted in a fixed-bedsystem. The particular choice of catalyst forms no essential part of myinvention, and a greatly detailed discussion thereof is not necessary toa clear understanding of the manner in which the present process iseffected. There are, however, certain aspects relative to the catalyticcomposites which are distinctly preferred. For example, although thecatalytic composite may be the same in all three of the reaction zones,in view of the fact that the functions serve thereby are distinctlydifferent one from the other, a preferred method utilizes catalystshaving similar, but different characteristics. In general, the processmakes use of catalytic composites having a hydrogenation/dehydrogenationfunction, coupled with a cracking function. Dual-function catalysts arethoroughly described in the literature, and are utilized for the purposeof promoting a wide variety of hydrocarbon conversion reactions. It isgenerally thought that the cracking function is associated with anacid-acting carrier material of a porous, adsorptive, refractoryinorganic oxide type. The carrier material is utilized as the supportfor one or more heavy metal components, generally the metals orcompounds of metals of Groups V through VIII of the Periodic Table.

It is well-known to those skilled in the art, that the principal causeof catalytic deactivation, or instability, of such dual-functioncatalysts is principally associated with the fact that coke forms on thesurface of the catalyst during the course of the reaction. The cokestems from the formation of heavy, high molecular weight, solid orsemi-solid, hydrogen-poor carbonaceous material which reduces theeffectiveness of the catalyst by shielding the active sites from thematerial being processed. This difficulty is further compounded by thesimultaneous presence of aromatic hydrocarbons and nitrogeous compoundsin the fresh feed charge stock. As hereinbefore set forth, themononuclear aromatics, or their partially hydrogenated derivatives, canundergo condensation to produce polynuclear compounds, the latteractually functioning as a catalyst poison.

Catalytic composites suitable for use in the process of the presentinvention constitute a carrier material of the crystalline aluminasknown as gamma-, eta-, and thetaalumina, and which generally containother refractory inorganic oxides such as silica, zirconia, magnesia,etc. In general, the carrier preferably constitutes a mixture of aluminaand one of the aforementioned oxides. Thus, the carrier material maycomprise alumina containing from about 10% to about 90% by weight ofsilica. At the operating conditions utilized, the carrier materialemployed in the hydrocracking reaction zone will contain a greaterpercentage of silica; similarly, the carrier material utilized in thedenitrification reaction zone will contain a somewhat lesser quantity ofsilica, but greater than that utilized in the carrier material withinthe desulfurization reaction zone. The carrier material may becharacterized as amorphous or zeolitic, the latter including mordenite,faujasite, type A or type U molecular sieves, etc. With respect to thehydrocracking reaction zone, a particularly preferred carrier materialis a crystalline 'aluminosilicate of which at least about 90.0% byweight is zeolitic. The carrier material may be prepared in any suitablemanner, and may be activated prior to use by one or more treatmentsincluding drying, calcination, steaming, etc. Although generallyexisting in some combined form, the concentration of the catalyticallyactive metallic components is calculated on the basis of the elementalmetals. Suitable hydrocracking catalysts will contain from about 0.01%to about 30.0% by weight of one or more metals, or compounds thereof,from the groups of vanadium, chromium, iron, cobalt, nickel, niobium,molybdenum, technetium, ruthenium, rhodium, palladium, tantalum,tungsten, rhenium, osmium, iridium and platinum. Another constituent ofhydrocracking catalysts, suitable for use in the process of the presentinvention is a halogen component. While the precise form of associationof the halogen component of the carrier material is not accuratelyknown, it is customary in the art to refer to the halogen component asbeing combined with the carrier, or with the other ingredients of thecatalyst therein. Combined halogen may be either fluorine, chlorine,iodine, bromine or mixtures thereof; of these, fluorine and chlorine areparticularly preferrd. The halogen will be composited with the carriermaterial in such a manner as results in a final catalytic compositecontaining from about 0.1% to about 2.0% by weight of a halogencomponent, calculated as the element.

The metallic components may be incorporated within the catalyticcomposite in any suitable manner including co-precipitation orco-gellation with the carrier, ionexchange, or impregnation of thecarrier, and either after or before calcination. Following theincorporation of the metallic components, the carrier material is driedand subjected to a high temperature calcination or oxidation techniqueat a temperature of about 750 F. to about 1300 F. When a crystallinealuminosilicate is utilized as the carrier material, the upper limit forthe calcination step is about 1000 F.

One particularly preferred catalyst preparation technique involves thewater-free reduction of the calcined composite. This particular step isdesigned to insure a more uniform and finely divided dispersion of themetallic components throughout the carrier material. Substantially pureand dry hydrogen, containing less than 30.0 volume ppm. of water isutilized as the reducing agent. The reduced catalytic composite is thensubjected to a presulfiding technique to incorporate from about 0.05% toabout 0.50% by weight of sulfur, on an elemental basis, within the finalcatalytic composite.

With respect to the desulfurization catalyst, the carrier materialcontains an excess of alumina with respect to silica, for example, 88.0%by weight of alumina and 12.0% by weight of silica. For effectivedesulfurization, this carrier material may then be combined with 11.3%by weight of molybdenum, 4.2% by weight of nickel and 0.05% by weight ofcobalt.

With respect to the denitrification catalyst, the quantity of silica isgenerally increased, for example, 63.0% by weight of alumina and 37.0%by Weight of silica. A suitable catalyst, utilizing this carriermaterial, would include 2.0% by weight of nickel and 16.0% by Weight ofmolybdenum. In many instances, depending upon the concentration ofnitrogenous compounds, calculated as nitrogen, within the fresh feedcharge stock, the catalyst in the denitrification zone will be preparedfrom a carrier material also containing boron phosphate in amounts fromabout 2.0% to about 25.0% by weight.

As hereinbefore stated, the hydrocracking catalyst contains the greaterpercentage of silica in the carrier material. Thus, one suitablehydrocracking catalyst comprises a carrier material of 75.0% by weightof silica and 25 .0% by weight of alumina, with which is combined 5.0%by weight of nickel. Another suitable catalyst utilizing the 75/25silica alumina carrier material, has impregnated thereon about 0. 4% byweight of platinum. A particularly preferred hydrocracking catalystconsists of about 5.0% by weight of nickel on a high silica faujasite,crystalline aluminosilicate, of Which at least about 90.0% by weight iszeolitic.

The operating conditions, under which the process is conducted, willvary according to the physical and chemical characteristics of thecharge stock, as well as the desired end result. With the exception ofthe catalyst bed temperature, these operating conditions may be the samein each of the three reaction zones, or entirely different one from theother. The various reactions, hydrocracking, desulfurization anddenitrification, are effected at elevated pressures in the range of fromabout 500 to about 5,000 p.s.i.g., and preferably at some intermediatelevel of about 800 to about 3,500 p.s.i.g. A preferred techniqueconstitues serial flow through the three reaction zones, starting withthe hydrocracking reactor, and, therefore, the hydrocracking reactorwill normally function at a higher pressure level than the otherreaction zones. The latter will function at a slightly lower pressuredue to the pressure drop experienced as a result of fluid flow throughthe system. As utilized herein, operating temperature alludes to themaximum temperature of the catalyst within the reaction zone; this isalso commonly referred to as the reactor outlet temperature. Since theprincipal reactionsbeing effected are exothermic in nature, anincreasing temperature gradient is experienced as the material flowsthrough the catalyst bed, with the result that the outlet temperature ishigher than that at the inlet to the catalyst bed. A preferred techniquelimits the temperature increase to 100 F., or less, and this may bereadily accomplished through the use of conventional quench streams,either normally liquid or normally gaseous, being introduced at one ormore intermediate loci of the reaction zone. The maximum catalyst bedtemperature within the hydrocarcking reaction zone is within the rangeof about 800 F. to about 900 F., and higher than that in either of theother two reaction zones. The maximum catalyst bed temperature withinthe desulfurization, or second, reaction zone is within the range ofabout 700 F. to about 800 F., and higher than the maximum catalyst bedtemperature Within the third, or denitrification reaction zone. Thelatter has a maximum catalyst bed temperature confined Within the rangeof about 650 F. to about 725 :F. At these conditions, nitrogenouscompounds contained within the charge stock are converted tohydrocarbons and ammonia, with some conversion of sulfurous compounds tohydrogen sulfide and hydrocarbons. Furthermore, at least partialsaturation of aromatic hydrocarbons is eifected. The normally liquidproduct effluent, substantially free from nitrogenous compounds, issubjected to hydrocracking Without incurring the detrimental effect ofthe simultaneous presence of nitrogenous compounds and aromatichydrocarbons. The hydrocracked product effluent, containing high-boilingsulfurous compounds, is then subjected to desulfurization, thedesulfurized normally liquid product effluent being admixed with thecharge stock for introduction into the denitrification reaction zone.

Liquid hourly space velocities (defined as volumes of hydrocarbon chargeper hour per volume of catalyst disposed in the reaction zone) of fromabout 0.25 to about 10.0 are suitable, the lower range generally beingconsidered necessary for the heavier stocks. Hydrogen circulation ratewill be at least about 3,000 standard cubic feet per barrel, having anupper limit of about 50,000 standard cubic feet per barrel, based uponfresh feed. For the majority of feed stocks, hydrogen concentrations inthe range of 5,000 to 20,000 standard cubic feet per barrel willsufiice. As hereinafter indicated in the description of the accompanyingdrawing, the overall process is facilitated since the hydrogencirculation constitutes series-flow, starting with the hydrocrackingreaction zone. The overall process is further facilitated by the factthat the second and third reaction zones can be stacked with the freshfeed charge stock being introduced at a locus therebetween. This ineffect provides a quench stream for the material which has passedthrough the desulfurization zone, and which is at a temperature higherthan that desirable in the denitrification reaction zone.

Other operating conditions and processing techniques will be presentedin the following description of the accompanying drawing.

DESCRIPTION OF DRAWING In the drawing, only those vessels and linesnecessary for a clear understanding of the present process arepresented. Various valves, control valves, knock-out pots, compressors,heat-exchangers, and start-up lines have been eliminated from thedrawing. These as 'well as other miscellaneous appurtenances are wellwithin the purview of one possessing expertise in the art of petroleumrefining. Further, the drawing will be described in conjunction with acommercially-scaled unit processing a blend of gas oils in an amount of8,500 barrels per day. The intended object is to produce maximumquantities of a heptane-3 F. gasoline boiling range product.

The blended charge stock is a mixture of a virgin gas oil, a heavyvacuum gas oil, a light cycle oil and a heavy cycle oil having thefollowing gravities in API 37.6, 25.7, 22.5, and 17.4, respectively.Pertinent properties of the blended material are a gravity of 32.7 API,an initial boiling point of 374 F., at 50.0% volumetric distillationtemperature of 524 F. and an end boiling point of 791 F. The blendedcharge is contaminated by the presence of 3,150 p.p.m. of sulfur, 51p.p.m. of nitrogen and constitutes about 29.1% by volume aromatichydrocarbons.

A hydrocracked product effluent is Withdrawn from reactor 14, containingcatalyst bed 15, by way of line 16, at a temperature of about 850 F. Thecatalytic composite disposed within reactor 14 constitutes 5.0% byweight of nickel combined with a carrier material of 75.0% by Weight ofsilica and 25.0% by weight of alumina. Following its use as aheat-exchange medium, to decrease its temperature to a level of about650 F., the hydrocracked product efiluent continues through line 16,being introduced thereby into reactor 2. Reactor 2 is under an imposedpressure of about 1,450 p.s.i.g. and contains a catalyst bed 3 of 11.3%by weight of molybdenum, 4.2% by weight of nickel and 0.05% by weight ofcobalt combined with a carrier material of 88.0% by Weight of aluminaand 12.0% by weight of silica. Catalyst bed 3 is in an amount such thatthe liquid hourly space velocity of the material flowing therethrough isabout 2.4. The outlet temperature of catalyst bed 3 is about 750 F., andis quenched by the fresh feed charge stock entering by way of line 1, toa temperature of about 575 F. It should be noted that reactor 2 containsseparate and distinct beds of catalyst 3 and 4, and in a stackedposition. The charge stock in line 1 is introduced therebetween by wayof locus 5. The particular manner by which catalyst beds 3 and 4 areseparated in reactor 2, and the internal means by which the charge stockin line 1 and the product effluent from catalyst bed 3 are intimatelyadmixed, are not considered to be essential features of my invention.

Catalyst bed 4, the primary function of which is to effect thedenitrification of the charge stock entering line 1, and partialdesulfurization, especially of the lowerboiling components, constitutesa carrier material of 63.0% by weight of alumina and 37.0% by weight ofsilica, with which is combined 2.0% by weight of nickel and 16.0% byweight of molybdenum. The catalyst employed is in a quantity such thatthe liquid hourly space velocity, based upon the 8,500 barrels per dayof fresh feed charge stock only is about 2.4. The product eflluentemanating from catalyst bed 4 by way of line 6 is at a temperature of675 F. Following its use as a heatexchange medium, and further cooled toa temperature of about 110 F., the efiluent continues through line 6into cold separator 7. Cold separator 7 serves to provide a principallyvaporous phase rich in hydrogen, withdrawn by way of line 8, and anormally liquid product effiuent indicated as being withdrawn by way ofline 9. Although not indicated in the drawing, the ammonia, resultingfrom the conversion of nitrogenous compounds, may be readily removedfrom the product effluent of line 6 by the well-known technique ofinjecting water therein prior to introducing the same into coldseparator 7. Cold separator 7 is then equipped with a water dip-leg fromwhich the sour water containing ammonia is removed and transported tosuitable waste facilities. Thus, the normally liquid portion of theproduct effluent in line 9 is substantially free from absorbed ammonia.The hydrogen-rich vaporous phase in line 8 may be suitably treated byany well-known means for the purpose of removing therefrom hydrogensulfide resulting from the conversion of the lower-boiling sulfurouscompounds in the charge stock. Lower-boiling sulfurous compounds areconsidered to be those boiling within the gasoline boiling rangei.e. attemperatures below about 400 F. Following the removal of hydrogensulfide, the hydrogen-enriched vaporous phase is introduced into reactor14 by compressive means not indicated in the drawing. Reactor 14 ismaintained at a pressure of about 1,500 p.s.i.g. by way of a pressurecontrol valve also not indicated. Make-up hydrogen, required tocompensate for that consumed in the process and removed by way ofdissolution in the product streams, may be added at any point, and fromany suitable source such as a hydrogen-producing process. Conveniencedictates that the make-up hydrogen enter the process by way of line 8,in an amount such that the hydrogen circulation through reactor 14 is inan amount of about 8,400 standard cubic feet per barrel. Catalyst bed 15is utilized in an amount such that the liquid hourly space velocitytherethrough is of the order of about 0.65.

The normally liquid product eflluent from cold separator 7 continuesthrough line 9 into product separation facility 10. Product separationfacility 10 will obviously be designed to conform to the recovery of oneor more desired product streams. As indicated in the drawing,hydrocarbonaceous material boiling below heptane is removed by way ofline 11 as an overhead stream. The stream may be further separated toprovide a C /C concentrate suitable for use in motor fuel blending. Thedesired product, gasoline boiling from heptane to about 380 F., isremoved by way of line 12. A bottoms stream, comprising that portion ofthe product efi'luent boiling TABLE.PRODUCT YIELD AND DISTRIBUTIONWeight, Volume, Component percent percent Ammonia Of interest is thefact that the foregoing product yield and distribution was obtained witha total chemical consumption of hydrogen of only 1,617 standard cubicfeet per barrel (2.84% by weight). Of further interest is the fact thatthe 18.36% by volume butanes produced constituted 70.0% iso-butane. Thetotal pentane/ hexane fraction has a gravity of about 833 API and aresearch octane rating (clear) of 85, the research octane rating (3 ml.TEL.) of 99. The desired gasoline fraction indicates a gravity of 53.2API, a research octane rating (clear) of 64, a research octane rating (3ml. TEL.) of 82, and consists of about 36.0% by volume parafiins, 52.0%by volume naphthenes and 12.0% by volume aromatics. It will berecognized that this type of gasoline boiling range fraction forms anexcellent charge for a catalytic reforming unit in order to increase theoctane rating thereof.

The foregoing specification, and particularly the example integratedinto the description of the drawing, clearly illustrates the method ofeffecting the process of the present invention, and indicates thebenefits to be afforded through the utilization thereof.

I claim as my invention:

1. A catalytic process for converting a sulfurous charge stock,containing nitrogenous compounds and aromatic hydrocarbons, intolower-boiling hydrocarbon products of predetermined end boiling point,which process comprises the steps of:

(a) reacting a substantially nitrogen-free portion of said charge stock,and hydrogen in a first reaction zone, in contact with a first catalyticcomposite, at conversion conditions including a maximum catalyst bedtemperature of 800 F. to about 900 F.;

(b) introducing the resulting first zone eflluent into a second reactionzone, and reacting the same and hydrogen, in contact with adesulfurization second catalytic composite, at desulfurizationconditions including a maximum catalyst bed temperature of 700 F. toabout 800 F.;

(c) introducing said charge stock and the resulting total second zoneeffluent into a third reaction zone, and reacting the same and hydrogen,in contact with a third catalytic composite, at conditions including amaximum catalyst bed temperature of about 650 F.

to about 725 F and selected to convert nitrogenous compounds;

(d) separating the third reaction zone eflluent to provide ahydrogen-rich vaporous phase, to recover said lower-boiling products andto provide a normally liquid stream boiling above said predetermined endboiling point and containing said nitrogen-free porton of said chargestock; and, (e) reacting said normally liquid stream in said firstreaction zone. 2. The process of claim 1 further characterized in thatsaid first catalytic composite contains a Group VIII metal componentcombined with a siliceous carrier material.

3. The process of claim 1 further characterized in that said and thirdcatalytic composites contain at least one metal component from themetals of Groups VI-B and the Iron-group.

4. The process of claim 1 further characterized in that said firstcatalytic composite contains a Group VIII metal component combined witha crystalline aluminosilicate carrier material.

5. The process of claim 1 further characterized in that the maximumcatalyst bed temperature is lower in said third reaction zone than insaid second reaction zone.

6. The process of claim 1 further characterized in that said hydrogenflows serially through said first, second and third reaction zones.

References Cited UNITED STATES PATENTS 6/1966 Hass et al. 20889 8/1967Wood 208-97 U.S. Cl. X.R.

